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Date:   Wed, 11 Mar 2020 11:49:54 -0700
From:   Kees Cook <keescook@chromium.org>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Jann Horn <jannh@google.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Bernd Edlinger <bernd.edlinger@hotmail.de>,
        Jonathan Corbet <corbet@lwn.net>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Andrei Vagin <avagin@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
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        Yuyang Du <duyuyang@gmail.com>,
        David Hildenbrand <david@redhat.com>,
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        David Howells <dhowells@redhat.com>,
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        Shakeel Butt <shakeelb@google.com>,
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        Christian Kellner <christian@kellner.me>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        Arnd Bergmann <arnd@arndb.de>,
        Sargun Dhillon <sargun@sargun.me>
Subject: Re: [PATCH] pidfd: Stop taking cred_guard_mutex
Message-ID: <202003111148.19578AA@keescook>
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On Tue, Mar 10, 2020 at 03:57:35PM -0500, Eric W. Biederman wrote:
> So ptrace_attach and seccomp use the cred_guard_mutex to guarantee
> a deadlock.

Well, that's the result, but seccomp uses it because it wants to
be certain that credentials and no_new_privs are changed together
"atomically".

-- 
Kees Cook